DE2831293A1 - METHOD FOR PRODUCING SINTERED HARD METALS AND DEVICE FOR CARRYING OUT THIS METHOD - Google Patents

Description

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»·. = π α 1 η r f s I r κ Π π 2 1 - 2 2 Telephone 089/29 84

Sumitomo Electric Industries, Ltd.
15, 5-chome, Kitahama, Higashi-ku, Osaka, Japan

Process for the production of sintered hard metals and device for carrying out this process

80988S / 08S8

Process for the production of sintered hard metals and device for carrying out this process

The invention relates to a method for producing sintered hard metals, in particular of cemented carbides, and a device for carrying out this method, in particular during sintering of cemented carbides reduces the variation in product quality which was previously unavoidable in the known vacuum sintering in the production of cemented carbides.

Cemented carbides are used in a conventional manner made of powder metallurgy. As a starting material, a powder mixture is first pressed and, if necessary, pre-sintered and processed and finally subjected to a final sintering treatment at 1,300 to 1,500.degree. In this way one can essentially get a pore-free product. There is a large scatter range for the product qualities produced by this process, which in the mainly due to the presence of carbon (hereinafter referred to as carbon content) during the manufacturing process is. In this respect, this carbon content must be precisely controlled. Of the permissible range of this carbon content is less than 3% the amount of carbon present in the cemented carbide. When the carbon content is too low in the cemented carbide, a so-called η phase results, which leads to embrittlement. When the carbon content is high, there will be excretion of free carbon. Slight differences in carbon content make one sizeable Influence on the quality and properties of the cemented carbide even if the carbon content is within the allowable range.

8919 809865/0

The conventional way of sintering is to use a vacuum sintering process used, in which, however, it is difficult to obtain cemented carbides with a constant carbon content or carbon content. The reason this is as follows: Different starting powders for cemented carbides are finely ground and the mixed powder (hereinafter referred to as "starting powder mixture" referred to), which is obtained in a wet process in a ball mill, has an extremely fine grain size,

2 and the specific surface area is up to a few m / g. One of those fine powder, when exposed to air, is easily oxidized by oxygen and the moisture present in the air, These difficulties are known in detail, including on Akio Hara: Study on Oxidation of Starting Material Powders for Cemented Carbides in Air at Normal Temperature in "Funtai oyobi Funmatsu Yakin (Journal of the Japan Society of Powder and Powder Metallurgy) ", Vol. 17, No. 8, Page 338 (1971) is referenced. From this reference it can be seen that that the oxidation of the powder is a kind of rusting with the formation of hydroxides in air. When heated during vacuum sintering this hydroxide is reduced by carbon. As a result, the carbon content is reduced during sintering. This carbon reduction depends on the amount of hydroxide present. Since the formation of the hydroxides are also influenced by the weather the carbon content in the finished product depends on the weather fluctuations. Although the starting powder mixture has been treated extremely iiorgfäitig so far, however, variations in terms of the quality of the end product cannot be sufficiently suppressed by vacuum sintering.

A method of preventing the carbon content from falling through Hydroxide reduction using hydrogen is effective in some respects, but it does result

⁸⁹¹⁹ B09885 / 0898

Nevertheless there are still quality variations for the following reasons:

The first reason arises from the following reduction reaction (1):

H ₂₊ (O) - ^ H ₂ O (1)

In this equation, (O) means oxygen in the hydroxides and oxides, respectively. The course of this reaction depends on the value of P _x . ^ / P ™ off.

H ₂ OH ₂

In this respect, it is necessary to increase the purity of the hydrogen which is fed to the sintering furnace (ie to lower the H "0") in order to obtain a sufficient reaction. Since H "0 is generated in the reaction, the hydrogen atmosphere has little reducing effect even if H _{2 is used} with high purity if H" 0 is not eliminated in a timely and rapid manner to a sufficient extent

will. As already mentioned above, the starting powder mixture for the cemented carbide has an extremely small grain size, so that a pack of this powder represents a body with extremely fine pores. The hydroxides arise on the pore walls (inner surfaces). In order to achieve a sufficient reducing effect in the pores, it is necessary _{to remove H 0} O quickly and to introduce H 2. When using conventional hydrogen furnaces, the movement or the transport of H _{1 cannot be carried out to a sufficient extent, so that the reduction by H 0 is} not obtained to a sufficient extent.

The second reason is based on and is based on the following reaction (2) attributable to the fact that the compact and pre-sintered body contains carbon and that furnace parts made of carbon are used in the furnace:

C + 2H ₂ ^ - * CH ₄ (2)

The reaction proceeds towards the right side at 600 ° C or a lower temperature at a total pressure of 1 atm. this

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corresponds to a carbon removal for the compact to be sintered Body. The reaction proceeds to the left at a temperature of 600 C or higher. This corresponds to a carburization. It's tough, to keep the temperature in the oven uniform at all oven locations. The flow of hydrogen gas is also often non-uniform. Therefore, both decarburization and carburization can occur. In this respect, there is a considerable variation in quality depending on the position in the furnace. The control or reduction of this quality variation is difficult.

The third reason is due to the following decarburization reaction (3) 900 ° C or higher:

H ₂ O + C— »CO + H ₂ (3)

In this case, the H «G represents a problem which was not introduced as an impurity in the hydrogen, but which _{arose as a result of the reduction or separately from the absorbed H 3} O in the furnace. The above-mentioned three reactions are intricately related and the control of these reactions is much more difficult than in the case of a vacuum furnace. In particular, reactions (2) and (3) have a disadvantageous effect at high temperatures due to the presence of hydrogen gas itself. In this respect, hydrogen sintering has only been used extremely rarely in recent times.

The object of the invention is to provide a method for the production of cemented carbides, in particular cemented carbide alloys, in which there is a dispersion in the quality and properties of the product is reduced, which must inevitably be accepted in conventional processes in the vacuum sintering.

809885/0898 8919

To solve this problem, the invention proposes that to generate of cemented carbide initially sintered a densely packed or pressed powder material as the starting material for the cemented carbide and then some or all of the heating and cooling steps are performed in both hydrogen and carbon monoxide atmospheres will.

The invention can be carried out in such a way that a packing is sintered from a starting material for the cemented carbides or a body formed from the package is sintered by pre-sintering and that, if necessary, processing of this pre-sintered Body and eventually some or all of the heating and cooling steps in both hydrogen and carbon monoxide atmospheres be performed.

The invention is particularly suitable for the production of sintered Hard metal alloys, in particular sintered carbides or carbonitrides.

When carrying out the sintering process according to the invention, effectively control the carbon content.

The invention also shows a device for producing cemented carbides, in particular of sintered carbides or carbonitrides, with which the sintering can be carried out in such a way, that a packing of the hard metal to be sintered or a shaped body from this packing is treated by pre-sintering and, if necessary, machined and possibly subjected to a shaping treatment. This is a part or all of the heating and cooling sections carried out both in a hydrogen atmosphere and in a carbon monoxide atmosphere. For this purpose, the furnace can be sintered with the

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densely packed material can be supplied and the furnace can have a gas inlet and have a gas outlet and an exhaust port. The gas flow or the flow rate of the gas in the furnace or in the furnace in can be controlled by a valve provided in the gas inlet. The internal pressure of the furnace can be controlled by a valve which is provided between the gas outlet and the exhaust port. The heating and cooling steps can be performed at a specific Flow rate of the gas and a certain pressure can be carried out.

The accompanying drawings serve to further explain the invention. Show it:

Fig. 1 is a graph showing the change in carbon

material content of a sintered carbide alloy with hydrogen pressure changed in the furnace;

Fig. 2 is a graph showing the relationship between the

free energy of reaction C t- 2H „- ^ CH. and the Temperature;

Fig. 3 is a graph showing the relationship of the free

Energies of the reduction reactions when using carbon and hydrogen and the temperature;

Fig. 4 (a) are graphs showing the change in the amounts of

Carbon and oxygen when heat packs of WC-28T1C-12, 8Co and WC-IOCo carbides to be sintered will;

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5 shows a schematic representation of an exemplary embodiment of an apparatus with which the invention can be carried out, and

6 shows a schematic representation of the deflection of a sheet metal which is caused by sintering.

When sintering cemented carbides, especially carbides, the oxygen contained in the powder is reduced by carbon. So far one has tried this reduction with hydrogen or to carry out carbon monoxide and carbon. In this method, however, the reaction system is rather complicated, and it it has been found that sintering is the most stable in a vacuum. In the invention it is assumed that a drastic Modification of the sintering process is necessary to facilitate control of the carbon content, and fundamental studies have been made employed in the elimination of gases and the diffusion of gases in dense packings of carbides to be sintered, which are available in grain sizes in the μm range. It turned out that vacuum is not always the most suitable measure for removing the gases.

When gas is generated in a tight packing, it will pass through the pores with a diameter of 1 μm or less and arrives thus outside of the tight packing. However, difficulties arise in this regard in a vacuum, since the mean free path of the gas is increased. By reducing the pressure, however, the mean free path is increased, so that a still relatively high pressure is desired is. When the furnace inside is at a reduced pressure using a gas such as

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Hydrogen or carbon monoxide, is maintained between a counter-diffusion of the generated gas and a supplied gas. The gas diffusion coefficient D obeys the following relationship:

D ~ l / P (P: pressure).

A low pressure is therefore desirable in this case.

This means that the rate of reduction in such pores is influenced by the mean free path of the gas and by the gas diffusion coefficient. In this respect, this is the rate of reduction highest for a given pressure range. It has been found that this pressure range is from 10 torr to 300 torr enough.

Furthermore, it has been found that when a large amount of gas is supplied to the furnace, a large amount of product gas (H ₂ O in the case of H ₀ , CO 2 in the case of CO) is generated rapidly, which in turn causes oxidation in the pores. To prevent this, it is necessary to reduce the gas concentration and achieve a gradual reaction. The reduction is preferably carried out under reduced pressure.

When sintering cemented carbides, in particular carbides, it is important that both the oxygen present in the powder is removed and carburization by the surrounding atmosphere is prevented. When a large amount of reducing gas (H ₀ , CO) is introduced into the sintering furnace, carburization occurs in some cases by the ambient atmosphere. This can be suppressed by reducing the gas concentration.

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From the above it follows that the control of the surrounding Atmosphere at reduced pressure for sintering fine powders, which are used as starting powder mixtures for cemented carbides, in particular Carbide used is suitable. Based on this knowledge, the invention shows a sintering technique that produces advantages and effects, which you get with sintering in a hydrogen stream or with sintering in vacuum and with combined sintering in hydrogen and Vacuum did not expect.

In the invention, a pressed metal is used for the production of cemented carbides or densely packed powder body made of metallic hard materials sintered, with some or all of the heating steps and cooling steps be carried out in both hydrogen and carbon monoxide atmospheres. It can do the properties of the product exactly being controlled. In this process, the pressed or tightly packed powder starting material can be subjected to a presintering. If necessary, a shape processing or some other processing can also be carried out before the final sintering. A preferred one Implementation to achieve the cemented hard metals, in particular carbides or carbide alloys, consists in the fact that a tight packing is pre-sintered from the carbides or carbide alloys or a body formed therefrom. If necessary, the resulting product can be carried out. Some or all of the heating steps or temperature increase steps can be used in Hydrogen and carbon monoxide atmospheres can be carried out. In a device that is preferably used, a tight packing made of the hard materials, in particular carbides or carbide alloys or molded bodies produced therefrom, presintered. The pre-sintered material is subjected to processing, if necessary. The furnace, in which the densely packed or pressed powder starting material is introduced, has a gas inlet, a gas -

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outlet and an exhaust port. The flow rate of the gas in the furnace is controlled by a valve placed in the gas inlet. The internal pressure in the furnace is controlled by a valve that is between the gas outlet and the exhaust port is provided. The heating or the temperature increase is at a predetermined flow rate of the gas and a predetermined pressure.

Preferably, in the invention, the sintering is carried out in both hydrogen as well as in a carbon monoxide atmosphere at reduced pressure, particularly at a pressure of 300 Torr or less.

In a further preferred embodiment, a part or all steps to increase the temperature below a predetermined or up to a predetermined temperature of 800 - 1200 C. carried out in a hydrogen atmosphere, while some or all Temperature rise above this predetermined temperature are carried out in a carbon monoxide atmosphere.

In a further embodiment of the invention, the pressure of the hydrogen is K) Torr or more. The sintered hard metals or alloys which are obtained by the method described above generally contain hard metal alloys with a hard phase, which essentially consist of at least one of the substances selected from the group consisting of carbides, nitrides, carbonilrides , Borides and silicides of group IVa, Va and VIa of the elements (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) of the periodic table and mixtures thereof, as well as solid solutions. In addition, the cemented carbides contain a binder metal phase consisting essentially of at least one metal from the iron group.

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Such cemented hard metals are based in particular on a tungsten carbide or carbonitride base. A cemented carbide with tungsten

carbide skeleton contains the WC-Co system or another metal of the iron group. Optionally, carbides such as titanium, tantalum, niobium, hafnium, zirconium, chromium and vanadium can be present. The composition can be as follows: 70-96 % tungsten carbide and 4-30% cobalt or optionally up to 50 % tungsten carbide, which is replaced by one or more of the carbides, such as titanium, tantalum, niobium, hafnium, zirconium, chromium and Vanadium.

Essential advantages of the invention can be seen in the fact that "

(1) Sintering at a reduced pressure of 300 Torr or less

(2) a gas flow is maintained at reduced pressure and

(3) a combination of hydrogen and carbon monoxide atmospheres is used for one part or for all temperature increase steps.

As a result, the gas generated during the reaction is extremely mobile because the gas counter-diffusion coefficient D is inversely proportional to the pressure. If hydrogen at reduced Pressure is used, the hydrogen gas diffuses sufficiently through the pores of the pressed raw material and that into the Water generated in pores can escape from the pores by counter-diffusion with the hydrogen gas. Experimentally it has been found that it is possible to sufficiently reduce the gas diffusion in an industrial style Control dimensions and obtain sufficient reduction by setting the pressure to 300 Torr or below. If the Pressure is greater than 300 Torr, the removal of the in the pores generated water is not possible and this results in a noticeable reduction in the reducing effect.

8919 8G988S / Ü898 '

In addition, the advantage of an easier gas flow in the furnace is achieved. When the internal pressure in the furnace is 300 Torr or less, gas is continuously supplied to the furnace. The supply of the gas he follows only to activate the gas counter-diffusion in the furnace. If the gas is not supplied, the partial pressure of the HO im increases Furnace, which creates disadvantages. The gas composition can be controlled in terms of volume by continuously feeding of the gas, the exhaust gases can be controlled so that control of the partial pressure in the furnace is obtained.

Furthermore, the hydrogen atmosphere can preferably be used in the invention and applying the carbon monoxide atmosphere in two stages. The hydrogen atmosphere is preferably used for Eliminating the oxygen on the surface of the oxidized powder, while preferring the carbon monoxide atmosphere to eliminate the Oxygen inside the powder is used. In practicing the invention, the amount of decarburization is controlled by use suitable gas atmospheres of hydrogen and carbon monoxide in two stages. Consequently, the use of a single gas atmosphere has no effect. If, for example, the sintering is only carried out in a hydrogen atmosphere, a reduction only takes place at low temperatures up to 800 C. In addition, in particular at a temperature of up to 1,200 C and higher, result no benefits. Rather, the water that is formed by the reduction with hydrogen reacts with carbon (C + HgO -> CO + H "), from which decarburization results and the fluctuations in the Carbon content can be increased. This is a major disadvantage. It is therefore advantageous to feed hydrogen at 1,200 ° C or below it, and in particular to stop at 800 ° C to 1200 ° C. On the other hand, if the carbon monoxide is used at a lower temperature

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temperature supplies, carbon falls due to the reaction 2CO -> C η CO, from. It is therefore advantageous to use at least the carbon monoxide to a temperature range in which the carbon monoxide is stable. The temperature range within which carbon does not is excreted and the reduction can be carried out to a sufficient extent, is between 800 C and 1,200 C at reduced Pressure. In this respect, this can be brought into line with the supply of hydrogen or the interruption of the supply of hydrogen.

In this respect, the invention can control the variation in the carbon content noticeably suppress during sintering by working within a suitable temperature range, in particular between 800 C and 1. 200 ° C, switched from hydrogen atmosphere to carbon monoxide atmosphere during sintering.

In detail, the invention will now be based on the accompanying figures explained.

In Fig. 1 is the change in the carbon content in a cemented carbide, in particular a sintered carbide alloy, shown when the hydrogen partial pressure in the furnace changes. From the The graph shows that decarburization is most effectively suppressed at a hydrogen pressure of 5 - 300 Torr. This depends on the gas diffusion rate, the amount of hydrogen and the speed of reaction.

Fig. 2 shows the energy released by the reaction between hydrogen and carbon to form methane. From the graph it can be seen that with reduced pressure, the amount of

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standing methane is reduced and this shows that the carburization can be prevented, which is often a problem with known hydrogen furnaces.

3 shows the energies normally released with regard to which reaction is more likely to take place, namely the hydrogen reduction or the carbon monoxide reduction. The occurrence of the hydrogen reduction or the carbon monoxide reduction is determined by the partial pressure of H ₀ O in H and in particular by the ratio of

² 2

P _TT „/ P _TT in the pressed or tightly packed powder starting material H ₂ OH ₂

and due to the temperature range between 800 C and 1,200 C.

Fig. 4 shows the change in the amounts of carbon and oxygen, when the compacts for the cemented carbide to be produced are heated. This change in quantity is plotted against the extent of Decarburization and deoxidation for a WC-Co composition and a WC-TiC-Co composition. The TiC-containing composition shows a greater degree of decarburization and deoxidation at a temperature of 1,000 ° C and higher. This shows that the oxides of Ti, Ta, Nb, etc. are difficult to reduce with hydrogen, and accordingly the reduction with carbon monoxide is more favorable in many cases is. In these cases, it is therefore preferable to increase the partial pressure of the carbon monoxide and to achieve an effective reduction at high temperatures. For WC-Co containing compositions, the extent of reduction is less at high temperatures. In this respect, the partial pressure of carbon monoxide can be decreased for such compositions. When the oxygen is sufficient through hydrogen reduction can be eliminated, sufficient results are obtained even at a partial pressure for CO of 0.1 Torr or less. the Temperature at which the carbon monoxide gas can be supplied,

8919 8098 8 5/089

is preferably in a temperature range of 800-1,200 C. The temperature at which the addition of the carbon monoxide, however, stopped will change with the intended outcome. If the sintering atmosphere is constantly maintained uniformly, it is to be expected that that deformations during sintering can be avoided and uniform solidification is achieved. To gas off To remove an alloy, the gas supply is stopped when the Reduction is complete after a liquid phase has appeared. A high vacuum is then created in the system and an alloy is obtained with high quality.

In the present invention, therefore, the supply of hydrogen is at a low temperature range and the carbon monoxide intake in carried out over a high temperature range. Optionally, the hydrogen gas can be mixed with argon, nitrogen or other gases Application. The carbon monoxide gas can be mixed with hydrogen, Argon and small amounts of carbon dioxide and other gases are used. The addition of these gases can also be intermittent can be carried out with good results. If you switch from hydrogen gas to carbon monoxide gas, that can be done Evacuate the system without affecting the results obtained with the present invention. It is there however, it is advantageous to keep the carbon monoxide atmosphere at 1,200 C, to get the results expected from carbon monoxide.

The use of a gas atmosphere for cooling also has advantages. The cooling rate of the sintered body can due to increased thermal conductivity compared to cooling can be increased in a vacuum. In addition, the binder metal phase can be strengthened by rapid cooling. The hydrogen gas

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In this context, there is a relatively high thermal conductivity.

When producing a cemented carbide, especially from carbides, in accordance with the method of the present invention, products of extremely uniform quality are obtained. One in the known method Inevitably occurring brittle η-phase and the precipitation of free carbon can be suppressed in the invention. In addition, the bending force that normally occurs in known methods, which on products of great length occurs during sintering.

For performing the sintering process according to the invention is a device advantageous in which a continuous gas flow can be maintained and in which the internal pressure in the sintering furnace is reduced can be so that sufficient diffusion of the gas can be maintained in the furnace.

It is known to carry out sintering at a low temperature in a pulsating hydrogen atmosphere (Japanese Patent Application No. 62304/1974). It has been assumed that the H ₀ O formed in a compact to be sintered can be eliminated by pulsating pressure, the reducing _{effect of the H 0 also being} promoted. In addition, the reaction of H ₀ O should be with

ti a

C, which occurs when the partial pressure of H ₀ O is high, can be prevented. However, difficulties arise in practice. Namely, the sintering device must have a pulsation device. In addition, the furnace temperature is subject to strong fluctuations due to the pulsating hydrogen pressure in the furnace due to the relatively high thermal conductivity of hydrogen. You also need a relative

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complex control device to carry out the pulsation automatically to be able to.

On the other hand, in the invention, the reduction in one atmosphere can be performed at a pressure of 300 Torr or less.

A suitable device for carrying out the invention is shown as an exemplary embodiment shown in FIG. You win this device by additional auxiliary equipment, which is only a small one Bring effort. The gas flow rate is achieved by mounting a valve in the gas inlet of the vacuum furnace. The pressure in the furnace is controlled by a valve which is arranged in the gas outlet which is in communication with the exhaust port. The opening of the valve is controlled.

The following working examples and comparative examples are intended to the invention will be explained in more detail. In these exemplary embodiments, the percentages mean percentages by weight, unless it other dimensions are given.

example 1

As can be seen from FIG. 5, there are 5 supply lines on a vacuum sintering furnace connected with flow meters and valves 1, 2, 3, 4 for the gas inlet. Between the gas outlet and a vacuum pump 7 a further valve 6 is provided for precise pressure control in the furnace.

25 kg of a compact with a composition of WC-7 % Co, which is prepared from WC powder with a grain size of 3 μηα and CO with an average grain size of 1 μΐη and which has a presin-

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$ 2

has been subjected to treatment and shaping treatment placed on a graphite sheet in the vacuum furnace. This vacuum furnace has an inside diameter of 800 mm. As in the following As explained, difficulties may arise in storing the compact in a molding chamber. Graphite heating elements are used in the vacuum furnace used.

_2

The vacuum furnace is initially set to 10 Torr using the vacuum pump evacuated. Hydrogen at a pressure of 300 mm water column is then gradually passed through the gas inlet valve at a flow rate introduced into the oven at a rate of 10 l / min. During this time the exhaust valve remains fully open. Then the The exhaust valve gradually closed so that the pressure in the furnace was adjusted to 100 torr. The heating elements then become electrical heated up. At 1,000 ° C, the gas inlet valve is closed and that The exhaust valve is fully opened. The furnace system is then evacuated to 5 × 10 Torr or below. Thereupon the inlet valve opened for the carbon monoxide and the carbon monoxide is introduced at a flow rate of 2 l / min. The exhaust valve is gradually closed and the pressure in the furnace is adjusted to 50 torr. The temperature is increased to 1,400 C. The inlet valve is closed and the outlet valve is fully opened. The system is thereby reduced to a vacuum of 1 χ 10 Torr or evacuated underneath. This state is maintained for one hour and it is cooled in vacuo.

The sintered body thus obtained has uniform and excellent properties. In contrast, when the conventional vacuum sintering process is carried out, the result is uneven progressive decarburization and the formation of a brittle phase with a

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Probability of 50% and more.

In the following exemplary embodiments, similar procedures are implemented performed using the same device. The purity of the hydrogen used with a dew point of -31 C and the carbon monoxide is 99.9%.

Example 2

A powder with a composition of WC-IO% Co is in a Ball mill wet ground using acetone, which is subsequently is eliminated. Due to carelessness, water got into the powder, so that the powder was strongly moistened. After pressing the powder and performing the vacuum sintering, there is an increased decarbonization, which deteriorates Results.

In order to avoid this, an experiment is carried out using the apparatus of Example 1. Be in this attempt 300 g of the batch is used and during sintering, hydrogen with a flow rate of 3 l / min and carbon monoxide are also used at a flow rate of 0.5 l / min and an excellent sintered body is obtained. This attempt means an extreme case which normally does not occur. It is therefore to expect that a stable quality for all Sinterhartmetallkör will be achieved by performing the invention.

Example 3

The starting powder mixture has a composition of WC-IO % Co. This is produced from WC powder with a grain size of 0.5 μm and Co powder with a grain size of 1 μm. This is a

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extremely fine powder and has a BET value (specific surface

2
marriage) of 6 m / g. This powder is stored in air for one week and shaped into a shaped body of 15 × 15 × 10 mm (hexahedron). Sintering is carried out in two stages using a sintering furnace with an internal volume of 30 liters:

Procedure art

Heating condition the atmosphere

(A) Invention room temperature - > 1,000 ° CH "100 Torr 1 l / min

1,000 ° C 1,350 ° C

1,350 ° C 1.38O ⁰ C

(B) State of
technology

CO 20 Torr 0.5 l / min vacuum 5 10 Torr

Room temperature -> 1,100 ° C vacuum 3 χ 10 ~ Torr 1,100 ° C - »1,380 ° C vacuum 5 χ ίο" ² Torr

In the invention (A), the sintered body is good. At the stand technique (B) shows a brittle η phase.

Example 4

The starting powder mixture from Example 3 is used. Direct After the powder has been obtained, it is pressed into a hexahedron measuring 50 × 50 × 20 mm. Pre-sintering at 600 ° C is carried out. This is followed by deformation to a hexahedron of 15 15 χ 10 mm. 15 days pass from pre-sintering to Mold treatment.

The resulting moldings are according to the method of Example 3 sintered and compared with each other. The method according to the invention results in excellent sintered bodies while a brittle η phase appears in the processes according to the prior art.

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From the above Examples 3 and 4 it can be seen that the sintering Even with those used in Examples 3 and 4, even fine powder mixing can be performed stably fine powder mixtures the oxidation proceeds rapidly and with a conventional vacuum furnace and vacuum sintering process the production of sintered bodies from such powder mixtures presents difficulties.

Example 5

A composition of WC-8 % TiC-IO% Co is used as the starting powder mixture. This powder mixture is prepared from WC powder with a grain size of 2 μm, (Τΐ, WC) powder with a grain size of 3 m and Co powder with an average grain size of 1 μm. The powder mixture is pressed into a hexahedron of 15 χ 10 χ 10 mm. 100 test specimens are each sintered according to the following sintering process using a sintering furnace with an internal volume of 200 liters:

Procedure art

Heating condition the atmosphere

(A) Invention room temperature - > 1,000 ° CH, 100 Torr 1.5 l / min

LOOO ⁰ C 1,400 ° C

1,400 ° C

(B) State of the room temperature

1,200 ° C

technology

1,200 C 1,400 ° C

1,400 ° C

(C) Room temperature level

600 ° C

technology

600 ° C

1,400 ° C

CO 20 torr 3 l / min
Vacuum 1 χ 10 Torr

Vacuum 3 χ 10 "Torr _o

Vacuum 5 χ 10 Torr _2

Vacuum 1 χ 10 Torr

H "760 Torr 30 l / min

-1
Vacuum 1 χ 10 Torr

The properties of each obtained from the 100 specimens Sintered bodies are the following:

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Process type Good η-phase Precipitation Free carbon -

excretion

(A) 100 0 0

(B) 81 19 0

(C) 52 34 14

The table above shows that, in the case of the invention, all of the sintered bodies obtained from the test bodies have good properties. Using H ₂ at 760 Torr results in a large number of products with relatively poor properties. The absence of carbon is noticeable during vacuum sintering.

Example 6

100 cutting inserts, which were obtained according to Example 5, are subjected to a cutting test with the following conditions:

Tool: SCM 3

Cutting speed: 110 m / min
Forward and backward travel: 0.36 mm Cutting depth: 1.5 mm
Time: 20 minutes

Tool shape: SNG 432

The durability of the specimen is measured with a view to achieving it a flank wear of 0.25 mm or more. The following results are obtained:

Sample broken flank wear Flank wear

0.25mm or more less than 0.25mm

69 46

A. 0 2 B. 3 28 C. 16 38

₈₉₁₉ R 0 98 8 5/089 8

-M-

From Examples 5 and 6 it can be seen that with the invention sintered hard metal body which have uniform properties can be obtained. . The properties of the sintered bodies, which have been produced by known methods a large spread.

example Ί

The same WQ-I% C o powder as in Example 1 is used and sintered under the following conditions to. to investigate the influence of the pressure of the furnace atmosphere:

Room temperature 1,000 ° C

Vacuum of 3 χ 10 or less

-1

Torr

State of
Technique A

Invention B Hg 1 Torr 10 l / min

GH ₂ 5 torr 10 l / min

DH ₂ 50 torr 10 l / min

EH ₂ 100 torr 10 l / min

F H "300 Torr 10 l / min

State of

Technology GH ₉ 700 Torr 10 l / min

1,000 ⁰ C

1,400 ^° C

-2 vacuum of 5 χ 10 Torr or less

Co 50 torr 2 l / min

_2

Vacuum of 5 10 Torr or less

Using a sintering furnace with an internal volume of 100 liters 100 samples are sintered in hexahedron shape of 15 × 15 × 10 mm and the distribution of the carbon content in the sintered carbide bodies obtained investigated as a function of the pressures in the furnace. The main values and standard deviations of the carbon contents are as follows Table reproduced:

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80988S / G898

BCDEFG 5.72 5.73 5.72 5.72 5.72 5.75

O ₅ 08 0.02 0.03 0.02 0.03 0.15

As can be seen, the deviations in the carbon contents in the invention are relatively small, while in the known methods A and G these deviations are considerably greater.

Example B.

An outlet spal mixture with the same composition as in Example 1 is pressed in a Hessaederforai of 50 × 50 × 20 mm. There is a dam Vorsmfcertmg in vacuo at SOO performed ^0C. At-

v / ird θϊεθ Deformraig au hexahedra of 15 χ 15 χ 8 mm dehydrated. IS days have passed since the presidency. the in such a way aialready @ t © ai Profoem the isa example 7 are given SiaterverfaliirsE sintered after the carbon content is checked:

ABCDS FG

5, β1 I ₅ <S4 5.70 % Ί2 5.72 5.73 5.68

Staadard

... 0.20 0.18 0.03 0.02 0.03 0.02 0.24

deviation '' '' '

It can be seen from the results of Examples 7 and 8 that the scattering of the carbon contents is relatively small under pressure conditions of 5-300 Torr according to the invention. 95 % or more are in a range of + 0.03%. In the case of the known method A or in the case of the method using H.sub.1 at 1 atm, considerable results arise

Deviations. These results are consistent with those of the two

8919 8Q98SS / Q898

83

games 5 and 6. From this, the advantageous effect of the invention is too see.

Example 9

A starting powder mixture with a composition of WC-IO % Co is prepared from WC powder with a grain size of 1 μm and Co powder with a grain size of 1 μm. This powder mixture is pressed into a hollow cylinder with 50 φ χ 10 φ χ 50 mm. 20 specimens, which have been produced in this way, are sintered according to the following process:

Heating condition (A) Invention room temperature -

the atmosphere

1,000 ° C

1,000 ° C

1,380 ° C

(B) State of
technology

Room temperature

1,000 ⁰ C

1,000 ° C

1,380 ° C

H ₂ 100 torr 10 l / min CO 150 torr 3 l / min vacuum 3 χ 10 ~ torr vacuum 5 χ 10 torr

So far, there has been a partial excretion in such sintered products of free carbon by carburizing from a carbon sheet took place, so that the sintered products had to be discarded. the Number of partially carburized products, which according to the above sintering processes carried out are the following:

Simply 1 9

Double Q 6

Triple 0 11

From the above results it can be seen that free carbon is hardly found in the invention, while in the process according to the prior art, free carbon in frequent cases

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occurs. This means that the sintered body has extremely stable properties can be obtained with the invention.

Example 10

The mixture of Example 9 is used as the starting powder mixture. A thin sheet of 300 20 χ 5 mm is made by pre-sintering and forming. 10 such Specimens are sintered according to the sintering method of the invention (A) and after sintering processes according to the prior art (B). The number of unusable products is determined, with a view to the fact that a deflection Δΐ of 1, 5 mm and above, as shown in FIG. 6, is established.

(A) Invention 0

(B) State of the art 6

From the above results, it can be seen that the formation of unusable products can be suppressed in the present invention. With the known methods, a considerable number of unusable products occur with a probability of 50 % and more. In order to make the unusable products usable again, a high level of mechanical effort is necessary due to the high hardness of the sintered hard rivet. In this respect, the effort involved in producing the desired sintered products is considerably reduced with the invention. Sintered carbide bodies with the desired dimensions are obtained.

Example 11

As a starting powder mixture, a cermet composition of TiC-10 % Mo ₂ C-12 % Ni is prepared from TiC powder with an average grain size of 1 μm, Mo "C powder with an average grain size -

8919 8 0 98 8 5/089 8

size of 1 μπι and from an Nl powder with an average grain size of 0.8 μΐη. This powder mixture is pressed into a hexahedron of 15 15 π 8 mm. The test specimens obtained are sintered according to the following methods:

Heating condition

Invention. Room temperature - $ 000 C Hg 80 torr 2 l / min C-3> 1,380 ° C CO '20 torr 1 l / min

⁰ CxIh "vacuum 1 s 10 ° Torr

üjtand the ■ room temperature - * 1 »200 ° C vacuum § χ 10 Torr

1. 200 ° C - > t. 380 ° C vacuum 1 sl © " ¹ Torr

1,380 ° CxIh '. Vacuum 1 s 10 ° '

It is thereby ®ia Slater oven with © IAEM laaeavolamea voe Sun Life © ra comparable -. Turns "The Sinterprodiaktesi which have been obtained by the Irfindung, can be identified hem pores and sintered products köraien readily au cutting tools processed!" will. In the case of the simter bodies obtained from the state of the art, siad mum. Part of Porea with an average diameter of about Ii μm is present. These sintered products are not suitable for cutting tools.

A starting powder mixture with a composition of Cjr «Co ~ 20 Ni is prepared from a Cr «C« powder with a throughput grain

Δ Q

size of 4μΐη and from a Ni powder with an average grain size from 3 μι ». This powder mixture is made into a hexahedral shape "from 30 χ "30 s brought 20 mm and sintered by the following process:

309885/0898

- & Γ-

Heating condition the atmosphere

(A) Invention room temperature -> 1 000 C 100 torr Hg 10 l / min 1000 ° C - ■> 1450 ° C CO 10 Torr 1 l / min

(B) State of the art room temperature technology

1,450 ° C vacuum 5 χ lo " ² Torr

In the invention (A) only small voids are found in the sintered bodies obtained and these sintered bodies have a density of 99.9% and more of the theoretical density. In the sintered bodies obtained according to the prior art, a large number of cavities have been found and the density is about 96 % of the theoretical density.

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809885/0898

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Claims (15)

New phone number Ö Ä: _: .. 1: - + - "1 • i ■ -. ■ '■ ■ · r. ·. Η f ί η η 8 q / 2 9 8 4 B 2 claims: 1. Process for the production of cemented carbide bodies, in particular made of carbides, by sintering an optionally pre-pressed and pre-sintered powder material, characterized in that some or all of the heating steps and cooling steps performed during sintering in both hydrogen and carbon monoxide atmospheres will. 2. The method according to claim 1, characterized in that the pre-pressed material is subjected to a presintering and optionally subsequently a shaping of the presintered material is carried out. 3. The method according to claim 1 or 2, characterized in that that in the production of a cemented carbide from carbides, some or all of the heating steps and temperature increasing steps both can be carried out in both hydrogen and carbon monoxide atmospheres. 4. The method according to claim 3, characterized in that the pre-pressed material is pre-sintered and optionally the pre-sintered Material undergoes a shape processing before the final sintering is carried out. 5. The method according to any one of claims 1 to 4, characterized in that that the heating steps are carried out in a hydrogen and carbon atmosphere at reduced pressure. A 8919 -N / G $ 698 $ 6 / O890 ORIGINAL INSPECTED 6. The method according to any one of claims 1 to 5, characterized in that that the sintering is carried out under reduced pressure of 300 torr or less in water and carbon monoxide atmosphere. 7. The method according to any one of claims 1 to 6, characterized in that that the cooling is carried out in a vacuum. 8. The method according to any one of claims 1 to 7, characterized in that that part or all of the temperature increase steps in a temperature range less than 800 - 1,200 ° C in a hydrogen atmosphere and part or all of the temperature increasing steps at a higher temperature range in a carbon monoxide atmosphere be performed. 9. The method according to any one of claims 1 to 8, characterized in that that the hydrogen atmosphere has a pressure of at least 10 torr. 10. The method according to any one of claims 1 to 9, characterized shows that the hydrogen is used in a mixture, which contains at least one of the substances of the group consisting of argon, nitrogen and carbon monoxide. 11. The method according to any one of claims 1 to 10, characterized in, that the carbon monoxide is used in a mixture, which at least one of the substances of the group consisting of Contains hydrogen, argon and carbon dioxide. 12. The method according to any one of claims 1 to 11, characterized in that that the gas flow is maintained under reduced pressure during the sintering. 8919 8Q988S / Q898 13. The method according to any one of claims 1 to 12, characterized in that that the gas is continuously introduced into the sintering furnace and the pressure in the sintering furnace at a pressure of at most 300 Torr is held. 14. The method according to any one of claims 1 to 13, characterized in, that from the hydrogen atmosphere to the carbon monoxide atmosphere at a temperature between 800 ° C and 1,200 ° C is changed. 15. Device for the production of cemented carbide bodies, in particular from carbides, by sintering pressed hard material powder with a sintering furnace, to which the compacts are fed and the one Having a gas inlet, a gas outlet and an exhaust port, thereby characterized in that for controlling the flow rate of the gas in the furnace, a valve is arranged in the gas inlet and for control the pressure in the furnace between the gas outlet and the exhaust gas opening * voltage a valve is arranged, and that the heating and cooling during the sintering can be carried out at a predetermined flow rate of the gas and a predetermined pressure. 8919% O3 ES 5 /